Conventionally, a method in which a dopant is added during crystal growth by the MBE (Molecular Beam Epitaxy) method or the EFG (Edge-defined Film-fed Growth) method (see, e.g., PTLs 1 and 2) and a method in which a dopant is added to a grown β-Ga2O3-based single crystal by ion implantation (see, e.g., PTL 3) are known to dope a β-Ga2O3-based single crystal.